PERITONEUM. 
rived they finally separate, partially investing, as 
they do so, the transverse portion of the duode- 
num. Thus both layers reach the abdominal 
parietes along the continuous line of attachment 
of the splenic omentum and the transverse me- 
socolon ; the internal layer from this continuous 
line invests the pancreas and other parts behind 
the stomach, then the lobulus Spigelii, and thus 
is conducted to the posterior surface of the 
lesser omentum, from which we started. The 
external layer of the omental sac, having reached 
this line of parietal attachment as part of the 
splenic omentum to the left, passes off on the 
left kidney and the lateral abdominal parietes 
and diaphragm ; having reached it below as 
the transverse mesocolon, it may thence be 
traced downwards to the root of the mesentery. 
The small intestine is enclosed in the extre- 
mity of the fold of a duplicature of peritoneum. 
That part of the fold which extends across from 
the posterior parietes to the intestine is called 
the mesentery. The two component layers of 
_ the mesentery are adherent by their apposed 
surfaces, except where vessels, &c. intervene, so 
that it is a parieto-visceral sheet with two free 
surfaces. The parietal attachment of the me- 
sentery is called its root, and extends obliquely 
across the spine from the left side of the second 
lumbar vertebra, where the duodenum emerging 
from the root of the transverse mesocolon be- 
comes jejunum, to the right iliac fossa, where 
the ilium enters the cecum. Though the pa- 
rietal attachment or root of the mesentery is but 
a few inches in length, its visceral attachment 
by means, of numerous ample foldings, like a 
ruffle, corresponds in length with the twenty 
feet of small intestine. Tracing, then, the peri- 
toneum heretofore forming the external layer of 
the great omental sac from the point where it 
reaches the posterior parietes as part of the 
transverse mesocolon, downwards, we come to 
that side of the root of the mesentery which 
looks upwards and to the right; thence we 
trace this surface continuous along the mesen- 
tery, over the bowel, back again along the other 
side of the mesentery, so reaching that side of 
its root whose aspect is downwards and.to the 
left; in both which directions the peritoneum 
may be traced onwards. To the left it reaches 
the right side of the descending colon, invests 
the front of that bowel, and passes off on the 
other side of it to the lateral parietes: occa- 
sionally only does it dip beneath the descending 
colon so as to come in contact with itself and 
form a mesentery for it, A little lower down, 
however, namely, in the leftiliac fossa, it always 
forms a mesentery for the sigmoid flexure of 
the colon, and, stilk lower down, for the first 
part of the rectum. The distinction, however, 
between iliac mesocolon and mesorectum, as 
the mesenteries of the sigmoid flexure and rec- 
tum are called, is quite arbitrary and unnatural ; 
a continuous mesenteric duplicature, broad in 
the middle and tapering to each end, serves to 
give attachment to both the sigmoid flexure and 
the first part of the rectum. Proceeding from 
the root of the mesentery downwards in the 
middle line, the peritoneum covers the sacro- 
vertebral prominence, and, just below, it ar- 
939 
rives at the rectum and forms a mesentery for 
its first portion as above stated. The perito- 
neum invests the front only of the second por- 
tion of the rectum, and at a variable distance 
from the anus quits it and extends across to the 
back of the bladder in the male, or vagina and 
uterus in the female, so that the lowermost por- 
tion of the rectum is destitute altogether of pe- 
ritoneal investment. 
From the other side of the root of the me- 
sentery, namely, that which looks upwards and 
to the right, we may trace the continuity of 
peritoneal surface off to the right lumbar region, 
investing the ascending colon in a like, and 
similarly variable, manner to that in which it 
was described as investing the descending co- 
lon ; and to the right iliac fossa, where it invests 
the cecum, sometimes, but not most frequently, 
forming a narrow mesentery for it called the 
meso-cecum. A bit of mesentery is usually 
afforded to the vermiform process, but this, of 
course, we do not reach by proceeding off late- 
rally from the last-mentioned aspect of the root 
of the mesentery. 
As mentioned above, the peritoneum extends 
across from the front of the rectum to the back 
of the bladder, in the male subject; the level 
at which it does so varies with the state of full- 
ness or emptiness of the bladder, and also is 
said to vary, ceteris paribus, in different indi- 
viduals ; frequently it is so low that the peri- 
toneum, passing across, touches the prostate. 
This is in the middle, between the front of the 
rectum and back of the bladder, but laterally 
the peritoneum is elevated into two antero- 
posterior folds, which extend across from the 
sides of the rectum to the sides of the bladder; 
these are called the recto-vesical folds or pos- 
terior ligaments of the bladder: anterior and 
external to them there are two other small 
folds. External to the recto-vesical folds the 
peritoneum does not descend nearly so low as 
it does between them; and therefore there is a 
remarkable, deepish, cul-de-sac, of -the same 
breadth as the rectum, between that intestine 
and the bladder. 
The posterior and lateral aspects and fundus 
of the bladder are invested with peritoneum, 
but not its anterior aspect: the peritoneum 
passes from the fundus of the bladder, by an 
even slant, on to the anterior abdominal pari- 
etes, not making any dip in front of it except 
when it is much distended. In the female 
there is a deep cul-de-sac of peritoneum be- 
tween the rectum and uterus, descending low 
enough to be in contact with the vagina : 
between the uterus and bladder there is a 
second but much shallower cul-de-sac. 
We have now traced the peritoneum over 
the ascending and descending portions of the 
colon to the abdominal parietes in the right 
and left lumbar region; from the recto-vesical 
folds and sides of the bladder to the iliac 
fosse ; and from the fundus of the bladder to 
the anterior abdominal parietes of the hy 
gastric region; from all or any of these posi- 
tions, or from any point between them, we 
may trace the peritoneal free surface uninter- 
ruptedly up to our first starting point, the 
